diff --git a/src/calibre/devices/mtp/windows/wpd.cpp b/src/calibre/devices/mtp/windows/wpd.cpp
index 15cdd51e22..867ce6bcee 100644
--- a/src/calibre/devices/mtp/windows/wpd.cpp
+++ b/src/calibre/devices/mtp/windows/wpd.cpp
@@ -120,14 +120,14 @@ wpd_enumerate_devices(PyObject *self, PyObject *args) {
         hresult_set_exc("Failed to get list of portable devices", hr);
     }
 
+    Py_BEGIN_ALLOW_THREADS;
     for (i = 0; i < num_of_devices; i++) {
-        Py_BEGIN_ALLOW_THREADS;
         CoTaskMemFree(pnp_device_ids[i]);
-        Py_END_ALLOW_THREADS;
         pnp_device_ids[i] = NULL;
     }
     free(pnp_device_ids);
     pnp_device_ids = NULL;
+    Py_END_ALLOW_THREADS;
 
     return Py_BuildValue("N", ans);
 } // }}}